doc/help/api-filter.html

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 342 <div class='body'>
 343 <!--
 344   "$Id$"
 345
 346   Filter and backend programming header for the Common UNIX Printing System
 347   (CUPS).
 348
 349   Copyright 2008-2009 by Apple Inc.
 350
 351   These coded instructions, statements, and computer programs are the
 352   property of Apple Inc. and are protected by Federal copyright
 353   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 354   which should have been included with this file.  If this file is
 355   file is missing or damaged, see the license at "http://www.cups.org/".
 356 -->
 357
 358 <h1 class='title'>Filter and Backend Programming</h1>
 359
 360 <div class='summary'><table summary='General Information'>
 361 <thead>
 362 <tr>
 363         <th>Headers</th>
 364         <th>cups/backend.h<br>
 365         cups/sidechannel.h</th>
 366 </tr>
 367 </thead>
 368 <tbody>
 369 <tr>
 370         <th>Library</th>
 371         <td>-lcups</td>
 372 </tr>
 373 <tr>
 374         <th>See Also</th>
 375         <td>Programming: <a href='api-overview.html' target='_top'>Introduction to CUPS Programming</a><br>
 376         Programming: <a href='api-cups.html' target='_top'>CUPS API</a><br>
 377         Programming: <a href='api-ppd.html' target='_top'>PPD API</a><br>
 378         Programming: <a href='api-raster.html' target='_top'>Raster API</a><br>
 379         Programming: <a href='postscript-driver.html' target='_top'>Developing PostScript Printer Drivers</a><br>
 380         Programming: <a href='raster-driver.html' target='_top'>Developing Raster Printer Drivers</a><br>
 381         Specifications: <a href='spec-design.html' target='_top'>CUPS Design Description</a></td>
 382 </tr>
 383 </tbody>
 384 </table></div>
 385 <h2 class="title">Contents</h2>
 386 <ul class="contents">
 387 <li><a href="#OVERVIEW">Overview</a><ul class="subcontents">
 388         <li><a href="#SECURITY">Security Considerations</a></li>
 389         <li><a href="#SIGNALS">Signal Handling</a></li>
 390         <li><a href="#TEMPFILES">Temporary Files</a></li>
 391         <li><a href="#COPIES">Copy Generation</a></li>
 392         <li><a href="#EXITCODES">Exit Codes</a></li>
 393         <li><a href="#ENVIRONMENT">Environment Variables</a></li>
 394         <li><a href="#MESSAGES">Communicating with the Scheduler</a></li>
 395         <li><a href="#COMMUNICATING_BACKEND">Communicating with the Backend</a></li>
 396         <li><a href="#COMMUNICATING_FILTER">Communicating with Filters</a></li>
 397         <li><a href="#SNMP">Doing SNMP Queries with Network Printers</a></li>
 398 </ul></li>
 399 <li><a href="#FUNCTIONS">Functions</a><ul class="code">
 400         <li><a href="#cupsBackChannelRead" title="Read data from the backchannel.">cupsBackChannelRead</a></li>
 401         <li><a href="#cupsBackChannelWrite" title="Write data to the backchannel.">cupsBackChannelWrite</a></li>
 402         <li><a href="#cupsBackendDeviceURI" title="Get the device URI for a backend.">cupsBackendDeviceURI</a></li>
 403         <li><a href="#cupsBackendReport" title="Write a device line from a backend.">cupsBackendReport</a></li>
 404         <li><a href="#cupsSideChannelDoRequest" title="Send a side-channel command to a backend and wait for a response.">cupsSideChannelDoRequest</a></li>
 405         <li><a href="#cupsSideChannelRead" title="Read a side-channel message.">cupsSideChannelRead</a></li>
 406         <li><a href="#cupsSideChannelSNMPGet" title="Query a SNMP OID's value.">cupsSideChannelSNMPGet</a></li>
 407         <li><a href="#cupsSideChannelSNMPWalk" title="Query multiple SNMP OID values.">cupsSideChannelSNMPWalk</a></li>
 408         <li><a href="#cupsSideChannelWrite" title="Write a side-channel message.">cupsSideChannelWrite</a></li>
 409 </ul></li>
 410 <li><a href="#TYPES">Data Types</a><ul class="code">
 411         <li><a href="#cups_backend_t" title="Backend exit codes">cups_backend_t</a></li>
 412         <li><a href="#cups_sc_bidi_t" title="Bidirectional capabilities">cups_sc_bidi_t</a></li>
 413         <li><a href="#cups_sc_command_t" title="Request command codes">cups_sc_command_t</a></li>
 414         <li><a href="#cups_sc_connected_t" title="Connectivity values">cups_sc_connected_t</a></li>
 415         <li><a href="#cups_sc_state_t" title="Printer state bits">cups_sc_state_t</a></li>
 416         <li><a href="#cups_sc_status_t" title="Response status codes">cups_sc_status_t</a></li>
 417         <li><a href="#cups_sc_walk_func_t" title="SNMP walk callback">cups_sc_walk_func_t</a></li>
 418 </ul></li>
 419 <li><a href="#ENUMERATIONS">Constants</a><ul class="code">
 420         <li><a href="#cups_backend_e" title="Backend exit codes">cups_backend_e</a></li>
 421         <li><a href="#cups_sc_bidi_e" title="Bidirectional capability values">cups_sc_bidi_e</a></li>
 422         <li><a href="#cups_sc_command_e" title="Request command codes">cups_sc_command_e</a></li>
 423         <li><a href="#cups_sc_connected_e" title="Connectivity values">cups_sc_connected_e</a></li>
 424         <li><a href="#cups_sc_state_e" title="Printer state bits">cups_sc_state_e</a></li>
 425         <li><a href="#cups_sc_status_e" title="Response status codes">cups_sc_status_e</a></li>
 426 </ul></li>
 427 </ul>
 428 <!--
 429   "$Id$"
 430
 431   Filter and backend programming introduction for CUPS.
 432
 433   Copyright 2007-2011 by Apple Inc.
 434   Copyright 1997-2006 by Easy Software Products, all rights reserved.
 435
 436   These coded instructions, statements, and computer programs are the
 437   property of Apple Inc. and are protected by Federal copyright
 438   law.  Distribution and use rights are outlined in the file "LICENSE.txt"
 439   which should have been included with this file.  If this file is
 440   file is missing or damaged, see the license at "http://www.cups.org/".
 441 -->
 442
 443 <h2 class='title'><a name="OVERVIEW">Overview</a></h2>
 444
 445 <p>Filters (which include printer drivers and port monitors) and backends
 446 are used to convert job files to a printable format and send that data to the
 447 printer itself. All of these programs use a common interface for processing
 448 print jobs and communicating status information to the scheduler. Each is run
 449 with a standard set of command-line arguments:<p>
 450
 451 <dl class="code">
 452
 453         <dt>argv[1]</dt>
 454         <dd>The job ID</dd>
 455
 456         <dt>argv[2]</dt>
 457         <dd>The user printing the job</dd>
 458
 459         <dt>argv[3]</dt>
 460         <dd>The job name/title</dd>
 461
 462         <dt>argv[4]</dt>
 463         <dd>The number of copies to print</dd>
 464
 465         <dt>argv[5]</dt>
 466         <dd>The options that were provided when the job was submitted</dd>
 467
 468         <dt>argv[6]</dt>
 469         <dd>The file to print (first program only)</dd>
 470 </dl>
 471
 472 <p>The scheduler runs one or more of these programs to print any given job. The
 473 first filter reads from the print file and writes to the standard output, while
 474 the remaining filters read from the standard input and write to the standard
 475 output. The backend is the last filter in the chain and writes to the
 476 device.</p>
 477
 478 <p>Filters are always run as a non-privileged user, typically "lp", with no
 479 connection to the user's desktop. Backends are run either as a non-privileged
 480 user or as root if the file permissions do not allow user or group execution.
 481 The <a href="#PERMISSIONS">file permissions</a> section talks about this in
 482 more detail.</p>
 483
 484 <h3><a name="SECURITY">Security Considerations</a></h3>
 485
 486 <p>It is always important to use security programming practices. Filters and
 487 most backends are run as a non-priviledged user, so the major security
 488 consideration is resource utilization - filters should not depend on unlimited
 489 amounts of CPU, memory, or disk space, and should protect against conditions
 490 that could lead to excess usage of any resource like infinite loops and
 491 unbounded recursion. In addition, filters must <em>never</em> allow the user to
 492 specify an arbitrary file path to a separator page, template, or other file
 493 used by the filter since that can lead to an unauthorized disclosure of
 494 information. <em>Always</em> treat input as suspect and validate it!</p>
 495
 496 <p>If you are developing a backend that runs as root, make sure to check for
 497 potential buffer overflows, integer under/overflow conditions, and file
 498 accesses since these can lead to privilege escalations. When writing files,
 499 always validate the file path and <em>never</em> allow a user to determine
 500 where to store a file.</p>
 501
 502 <blockquote><b>Note:</b>
 503
 504 <p><em>Never</em> write files to a user's home directory. Aside from the
 505 security implications, CUPS is a network print service and as such the network
 506 user may not be the same as the local user and/or there may not be a local home
 507 directory to write to.</p>
 508
 509 <p>In addition, some operating systems provide additional security mechanisms
 510 that further limit file system access, even for backends running as root. On
 511 Mac OS X, for example, no backend may write to a user's home directory.</p>
 512 </blockquote>
 513
 514 <h3><a name="SIGNALS">Signal Handling</a><h3>
 515
 516 <p>The scheduler sends <code>SIGTERM</code> when a printing job is canceled or
 517 held. Filters, backends, and port monitors <em>must</em> catch
 518 <code>SIGTERM</code> and perform any cleanup necessary to produce a valid output
 519 file or return the printer to a known good state. The recommended behavior is to
 520 end the output on the current page.</p>
 521
 522 <h3><a name="PERMISSIONS">File Permissions</a></h3>
 523
 524 <p>For security reasons, CUPS will only run filters and backends that are owned
 525 by root and do not have world or group write permissions. The recommended
 526 permissions for filters and backends are 0555 - read and execute but no write.
 527 Backends that must run as root should use permissions of 0500 - read and execute
 528 by root, no access for other users. Write permissions can be enabled for the
 529 root user only.</p>
 530
 531 <p>To avoid a warning message, the directory containing your filter(s) must also
 532 be owned by root and have world and group write disabled - permissions of 0755
 533 or 0555 are strongly encouraged.</p>
 534
 535 <h3><a name="TEMPFILES">Temporary Files</a></h3>
 536
 537 <p>Temporary files should be created in the directory specified by the
 538 "TMPDIR" environment variable. The
 539 <a href="#cupsTempFile2"><code>cupsTempFile2</code></a> function can be
 540 used to safely create temporary files in this directory.</p>
 541
 542 <h3><a name="COPIES">Copy Generation</a></h3>
 543
 544 <p>The <code>argv[4]</code> argument specifies the number of copies to produce
 545 of the input file. In general, you should only generate copies if the
 546 <em>filename</em> argument is supplied. The only exception to this are
 547 filters that produce device-independent PostScript output, since the PostScript
 548 filter <var>pstops</var> is responsible for generating copies of PostScript
 549 files.</p>
 550
 551 <h3><a name="EXITCODES">Exit Codes</a></h3>
 552
 553 <p>Filters must exit with status 0 when they successfully generate print data
 554 or 1 when they encounter an error. Backends can return any of the
 555 <a href="#cups_backend_t"><code>cups_backend_t</code></a> constants.</p>
 556
 557 <h3><a name="ENVIRONMENT">Environment Variables</a></h3>
 558
 559 <p>The following environment variables are defined by the printing system
 560 when running print filters and backends:</p>
 561
 562 <dl class="code">
 563
 564         <dt>APPLE_LANGUAGE</dt>
 565         <dd>The Apple language identifier associated with the job
 566         (Mac OS X only).</dd>
 567
 568         <dt>CHARSET</dt>
 569         <dd>The job character set, typically "utf-8".</dd>
 570
 571         <dt>CLASS</dt>
 572         <dd>When a job is submitted to a printer class, contains the name of
 573         the destination printer class. Otherwise this environment
 574         variable will not be set.</dd>
 575
 576         <dt>CONTENT_TYPE</dt>
 577         <dd>The MIME type associated with the file (e.g.
 578         application/postscript).</dd>
 579
 580         <dt>CUPS_CACHEDIR</dt>
 581         <dd>The directory where cache files can be stored. Cache files can be
 582         used to retain information between jobs or files in a job.</dd>
 583
 584         <dt>CUPS_DATADIR</dt>
 585         <dd>The directory where (read-only) CUPS data files can be found.</dd>
 586
 587         <dt>CUPS_FILETYPE</dt>
 588         <dd>The type of file being printed: "job-sheet" for a banner page and
 589         "document" for a regular print file.</dd>
 590
 591         <dt>CUPS_SERVERROOT</dt>
 592         <dd>The root directory of the server.</dd>
 593
 594         <dt>DEVICE_URI</dt>
 595         <dd>The device-uri associated with the printer.</dd>
 596
 597         <dt>FINAL_CONTENT_TYPE</dt>
 598         <dd>The MIME type associated with the printer (e.g.
 599         application/vnd.cups-postscript).</dd>
 600
 601         <dt>LANG</dt>
 602         <dd>The language locale associated with the job.</dd>
 603
 604         <dt>PPD</dt>
 605         <dd>The full pathname of the PostScript Printer Description (PPD)
 606         file for this printer.</dd>
 607
 608         <dt>PRINTER</dt>
 609         <dd>The queue name of the class or printer.</dd>
 610
 611         <dt>RIP_CACHE</dt>
 612         <dd>The recommended amount of memory to use for Raster Image
 613         Processors (RIPs).</dd>
 614
 615         <dt>TMPDIR</dt>
 616         <dd>The directory where temporary files should be created.</dd>
 617
 618 </dl>
 619
 620 <h3><a name="MESSAGES">Communicating with the Scheduler</a></h3>
 621
 622 <p>Filters and backends communicate with the scheduler by writing messages
 623 to the standard error file. The scheduler reads messages from all filters in
 624 a job and processes the message based on its prefix. For example, the following
 625 code sets the current printer state message to "Printing page 5":</p>
 626
 627 <pre class="example">
 628 int page = 5;
 629
 630 fprintf(stderr, "INFO: Printing page %d\n", page);
 631 </pre>
 632
 633 <p>Each message is a single line of text starting with one of the following
 634 prefix strings:</p>
 635
 636 <dl class="code">
 637
 638         <dt>ALERT: message</dt>
 639         <dd>Sets the printer-state-message attribute and adds the specified
 640         message to the current error log file using the "alert" log level.</dd>
 641
 642         <dt>ATTR: attribute=value [attribute=value]</dt>
 643         <dd>Sets the named printer or job attribute(s). Typically this is used
 644         to set the <code>marker-colors</code>, <code>marker-levels</code>,
 645         <code>marker-message</code>, <code>marker-names</code>,
 646         <code>marker-types</code>, <code>printer-alert</code>, and
 647         <code>printer-alert-description</code> printer attributes. Standard
 648         <code>marker-types</code> values are listed in <a href='#TABLE1'>Table
 649         1</a>.</dd>
 650
 651         <dt>CRIT: message</dt>
 652         <dd>Sets the printer-state-message attribute and adds the specified
 653         message to the current error log file using the "critical" log
 654         level.</dd>
 655
 656         <dt>DEBUG: message</dt>
 657         <dd>Sets the printer-state-message attribute and adds the specified
 658         message to the current error log file using the "debug" log level.</dd>
 659
 660         <dt>DEBUG2: message</dt>
 661         <dd>Sets the printer-state-message attribute and adds the specified
 662         message to the current error log file using the "debug2" log level.</dd>
 663
 664         <dt>EMERG: message</dt>
 665         <dd>Sets the printer-state-message attribute and adds the specified
 666         message to the current error log file using the "emergency" log
 667         level.</dd>
 668
 669         <dt>ERROR: message</dt>
 670         <dd>Sets the printer-state-message attribute and adds the specified
 671         message to the current error log file using the "error" log level.
 672         Use "ERROR:" messages for non-persistent processing errors.</dd>
 673
 674         <dt>INFO: message</dt>
 675         <dd>Sets the printer-state-message attribute. If the current log level
 676         is set to "debug2", also adds the specified message to the current error
 677         log file using the "info" log level.</dd>
 678
 679         <dt>NOTICE: message</dt>
 680         <dd>Sets the printer-state-message attribute and adds the specified
 681         message to the current error log file using the "notice" log level.</dd>
 682
 683         <dt>PAGE: page-number #-copies</dt>
 684         <dt>PAGE: total #-pages</dt>
 685         <dd>Adds an entry to the current page log file. The first form adds
 686         #-copies to the job-media-sheets-completed attribute. The second
 687         form sets the job-media-sheets-completed attribute to #-pages.</dd>
 688
 689         <dt>PPD: keyword=value [keyword=value ...]</dt>
 690         <dd>Changes or adds keywords to the printer's PPD file. Typically
 691         this is used to update installable options or default media settings
 692         based on the printer configuration.</dd>
 693
 694         <dt>STATE: printer-state-reason [printer-state-reason ...]</dt>
 695         <dt>STATE: + printer-state-reason [printer-state-reason ...]</dt>
 696         <dt>STATE: - printer-state-reason [printer-state-reason ...]</dt>
 697         <dd>Sets, adds, or removes printer-state-reason keywords to the
 698         current queue. Typically this is used to indicate persistent media,
 699         ink, toner, and configuration conditions or errors on a printer.
 700         <a href='#TABLE2'>Table 2</a> lists the standard state keywords -
 701         use vendor-prefixed ("com.acme.foo") keywords for custom states.
 702
 703         <blockquote><b>Note:</b>
 704
 705         <p>"STATE:" messages often provide visible alerts to the user. For example, on
 706         Mac OS X setting a printer-state-reason value with an "-error" or "-warning"
 707         suffix will cause the printer's dock item to bounce if the corresponding reason
 708         is localized with a cupsIPPReason keyword in the printer's PPD file.</p>
 709
 710         </blockquote></dd>
 711
 712         <dt>WARNING: message</dt>
 713         <dd>Sets the printer-state-message attribute and adds the specified
 714         message to the current error log file using the "warning" log
 715         level.</dd>
 716
 717 </dl>
 718
 719 <p>Messages without one of these prefixes are treated as if they began with
 720 the "DEBUG:" prefix string.</p>
 721
 722 <div class='table'><table width='80%' summary='Table 1: Standard marker-types Values'>
 723 <caption>Table 1: <a name='TABLE1'>Standard marker-types Values</a></caption>
 724 <thead>
 725 <tr>
 726         <th>marker-type</th>
 727         <th>Description</th>
 728 </tr>
 729 </thead>
 730 <tbody>
 731 <tr>
 732         <td>developer</td>
 733         <td>Developer unit</td>
 734 </tr>
 735 <tr>
 736         <td>fuser</td>
 737         <td>Fuser unit</td>
 738 </tr>
 739 <tr>
 740         <td>fuserCleaningPad</td>
 741         <td>Fuser cleaning pad</td>
 742 </tr>
 743 <tr>
 744         <td>fuserOil</td>
 745         <td>Fuser oil</td>
 746 </tr>
 747 <tr>
 748         <td>ink</td>
 749         <td>Ink supply</td>
 750 </tr>
 751 <tr>
 752         <td>opc</td>
 753         <td>Photo conductor</td>
 754 </tr>
 755 <tr>
 756         <td>solidWax</td>
 757         <td>Wax supply</td>
 758 </tr>
 759 <tr>
 760         <td>staples</td>
 761         <td>Staple supply</td>
 762 </tr>
 763 <tr>
 764         <td>toner</td>
 765         <td>Toner supply</td>
 766 </tr>
 767 <tr>
 768         <td>transferUnit</td>
 769         <td>Transfer unit</td>
 770 </tr>
 771 <tr>
 772         <td>wasteInk</td>
 773         <td>Waste ink tank</td>
 774 </tr>
 775 <tr>
 776         <td>wasteToner</td>
 777         <td>Waste toner tank</td>
 778 </tr>
 779 <tr>
 780         <td>wasteWax</td>
 781         <td>Waste wax tank</td>
 782 </tr>
 783 </tbody>
 784 </table></div>
 785
 786 <br>
 787
 788 <div class='table'><table width='80%' summary='Table 2: Standard State Keywords'>
 789 <caption>Table 2: <a name='TABLE2'>Standard State Keywords</a></caption>
 790 <thead>
 791 <tr>
 792         <th>Keyword</th>
 793         <th>Description</th>
 794 </tr>
 795 </thead>
 796 <tbody>
 797 <tr>
 798         <td>connecting-to-device</td>
 799         <td>Connecting to printer but not printing yet</td>
 800 </tr>
 801 <tr>
 802         <td>cover-open</td>
 803         <td>A cover is open on the printer</td>
 804 </tr>
 805 <tr>
 806         <td>input-tray-missing</td>
 807         <td>An input tray is missing from the printer</td>
 808 </tr>
 809 <tr>
 810         <td>marker-supply-empty</td>
 811         <td>Out of ink</td>
 812 </tr>
 813 <tr>
 814         <td>marker-supply-low</td>
 815         <td>Low on ink</td>
 816 </tr>
 817 <tr>
 818         <td>marker-waste-almost-full</td>
 819         <td>Waste tank almost full</td>
 820 </tr>
 821 <tr>
 822         <td>marker-waste-full</td>
 823         <td>Waste tank full</td>
 824 </tr>
 825 <tr>
 826         <td>media-empty</td>
 827         <td>Out of media</td>
 828 </tr>
 829 <tr>
 830         <td>media-jam</td>
 831         <td>Media is jammed in the printer</td>
 832 </tr>
 833 <tr>
 834         <td>media-low</td>
 835         <td>Low on media</td>
 836 </tr>
 837 <tr>
 838         <td>paused</td>
 839         <td>Stop the printer</td>
 840 </tr>
 841 <tr>
 842         <td>timed-out</td>
 843         <td>Unable to connect to printer</td>
 844 </tr>
 845 <tr>
 846         <td>toner-empty</td>
 847         <td>Out of toner</td>
 848 </tr>
 849 <tr>
 850         <td>toner-low</td>
 851         <td>Low on toner</td>
 852 </tr>
 853 </tbody>
 854 </table></div>
 855
 856 <h3><a name="COMMUNICATING_BACKEND">Communicating with the Backend</a></h3>
 857
 858 <p>Filters can communicate with the backend via the
 859 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> and
 860 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 861 functions. The
 862 <a href="#cupsBackChannelRead"><code>cupsBackChannelRead</code></a> function
 863 reads data that has been sent back from the device and is typically used to
 864 obtain status and configuration information. For example, the following code
 865 polls the backend for back-channel data:</p>
 866
 867 <pre class="example">
 868 #include &lt;cups/cups.h&gt;
 869
 870 char buffer[8192];
 871 ssize_t bytes;
 872
 873 /* Use a timeout of 0.0 seconds to poll for back-channel data */
 874 bytes = cupsBackChannelRead(buffer, sizeof(buffer), 0.0);
 875 </pre>
 876
 877 <p>Filters can also use <code>select()</code> or <code>poll()</code> on the
 878 back-channel file descriptor (3 or <code>CUPS_BC_FD</code>) to read data only
 879 when it is available.</p>
 880
 881 <p>The
 882 <a href="#cupsSideChannelDoRequest"><code>cupsSideChannelDoRequest</code></a>
 883 function allows you to get out-of-band status information and do synchronization
 884 with the device. For example, the following code gets the current IEEE-1284
 885 device ID string from the backend:</p>
 886
 887 <pre class="example">
 888 #include &lt;cups/sidechannel.h&gt;
 889
 890 char data[2049];
 891 int datalen;
 892 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 893
 894 /* Tell cupsSideChannelDoRequest() how big our buffer is, less 1 byte for
 895    nul-termination... */
 896 datalen = sizeof(data) - 1;
 897
 898 /* Get the IEEE-1284 device ID, waiting for up to 1 second */
 899 status = <a href="#cupsSideChannelDoRequest">cupsSideChannelDoRequest</a>(CUPS_SC_CMD_GET_DEVICE_ID, data, &amp;datalen, 1.0);
 900
 901 /* Use the returned value if OK was returned and the length is non-zero */
 902 if (status == CUPS_SC_STATUS_OK && datalen > 0)
 903   data[datalen] = '\0';
 904 else
 905   data[0] = '\0';
 906 </pre>
 907
 908 <h3><a name="COMMUNICATING_FILTER">Communicating with Filters</a></h3>
 909
 910 <p>Backends communicate with filters using the reciprocal functions
 911 <a href="#cupsBackChannelWrite"><code>cupsBackChannelWrite</code></a>,
 912 <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>, and
 913 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a>. We
 914 recommend writing back-channel data using a timeout of 1.0 seconds:</p>
 915
 916 <pre class="example">
 917 #include &lt;cups/cups.h&gt;
 918
 919 char buffer[8192];
 920 ssize_t bytes;
 921
 922 /* Obtain data from printer/device */
 923 ...
 924
 925 /* Use a timeout of 1.0 seconds to give filters a chance to read */
 926 cupsBackChannelWrite(buffer, bytes, 1.0);
 927 </pre>
 928
 929 <p>The <a href="#cupsSideChannelRead"><code>cupsSideChannelRead</code></a>
 930 function reads a side-channel command from a filter, driver, or port monitor.
 931 Backends can either poll for commands using a <code>timeout</code> of 0.0, wait
 932 indefinitely for commands using a <code>timeout</code> of -1.0 (probably in a
 933 separate thread for that purpose), or use <code>select</code> or
 934 <code>poll</code> on the <code>CUPS_SC_FD</code> file descriptor (4) to handle
 935 input and output on several file descriptors at the same time.</p>
 936
 937 <p>Once a command is processed, the backend uses the
 938 <a href="#cupsSideChannelWrite"><code>cupsSideChannelWrite</code></a> function
 939 to send its response. For example, the following code shows how to poll for a
 940 side-channel command and respond to it:</p>
 941
 942 <pre class="example">
 943 #include &lt;cups/sidechannel.h&gt;
 944
 945 <a href="#cups_sc_command_t">cups_sc_command_t</a> command;
 946 <a href="#cups_sc_status_t">cups_sc_status_t</a> status;
 947 char data[2048];
 948 int datalen = sizeof(data);
 949
 950 /* Poll for a command... */
 951 if (!<a href="#cupsSideChannelRead">cupsSideChannelRead</a>(&amp;command, &amp;status, data, &amp;datalen, 0.0))
 952 {
 953   switch (command)
 954   {
 955     /* handle supported commands, fill data/datalen/status with values as needed */
 956
 957     default :
 958         status  = CUPS_SC_STATUS_NOT_IMPLEMENTED;
 959         datalen = 0;
 960         break;
 961   }
 962
 963   /* Send a response... */
 964   <a href="#cupsSideChannelWrite">cupsSideChannelWrite</a>(command, status, data, datalen, 1.0);
 965 }
 966 </pre>
 967
 968 <h3><a name="SNMP">Doing SNMP Queries with Network Printers</a></h3>
 969
 970 <p>The Simple Network Management Protocol (SNMP) allows you to get the current
 971 status, page counter, and supply levels from most network printers. Every
 972 piece of information is associated with an Object Identifier (OID), and
 973 every printer has a <em>community</em> name associated with it. OIDs can be
 974 queried directly or by "walking" over a range of OIDs with a common prefix.</p>
 975
 976 <p>The two CUPS SNMP functions provide a simple API for querying network
 977 printers through the side-channel interface. Each accepts a string containing
 978 an OID like ".1.3.6.1.2.1.43.10.2.1.4.1.1" (the standard page counter OID)
 979 along with a timeout for the query.</p>
 980
 981 <p>The <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>
 982 function queries a single OID and returns the value as a string in a buffer
 983 you supply:</p>
 984
 985 <pre class="example">
 986 #include &lt;cups/sidechannel.h&gt;
 987
 988 char data[512];
 989 int datalen = sizeof(data);
 990
 991 if (<a href="#cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a>(".1.3.6.1.2.1.43.10.2.1.4.1.1", data, &amp;datalen, 5.0)
 992         == CUPS_SC_STATUS_OK)
 993 {
 994   /* Do something with the value */
 995   printf("Page counter is: %s\n", data);
 996 }
 997 </pre>
 998
 999 <p>The
1000 <a href="#cupsSideChannelSNMPWalk"><code>cupsSideChannelSNMPWalk</code></a>
1001 function allows you to query a whole group of OIDs, calling a function of your
1002 choice for each OID that is found:</p>
1003
1004 <pre class="example">
1005 #include &lt;cups/sidechannel.h&gt;
1006
1007 void
1008 my_callback(const char *oid, const char *data, int datalen, void *context)
1009 {
1010   /* Do something with the value */
1011   printf("%s=%s\n", oid, data);
1012 }
1013
1014 ...
1015
1016 void *my_data;
1017
1018 <a href="#cupsSideChannelSNMPWalk">cupsSNMPSideChannelWalk</a>(".1.3.6.1.2.1.43", 5.0, my_callback, my_data);
1019 </pre>
1020 <h2 class="title"><a name="FUNCTIONS">Functions</a></h2>
1021 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelRead">cupsBackChannelRead</a></h3>
1022 <p class="description">Read data from the backchannel.</p>
1023 <p class="code">
1024 ssize_t cupsBackChannelRead (<br>
1025 &nbsp;&nbsp;&nbsp;&nbsp;char *buffer,<br>
1026 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1027 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1028 );</p>
1029 <h4 class="parameters">Parameters</h4>
1030 <dl>
1031 <dt>buffer</dt>
1032 <dd class="description">Buffer to read into</dd>
1033 <dt>bytes</dt>
1034 <dd class="description">Bytes to read</dd>
1035 <dt>timeout</dt>
1036 <dd class="description">Timeout in seconds, typically 0.0 to poll</dd>
1037 </dl>
1038 <h4 class="returnvalue">Return Value</h4>
1039 <p class="description">Bytes read or -1 on error</p>
1040 <h4 class="discussion">Discussion</h4>
1041 <p class="discussion">Reads up to &quot;bytes&quot; bytes from the backchannel/backend. The &quot;timeout&quot;
1042 parameter controls how many seconds to wait for the data - use 0.0 to
1043 return immediately if there is no data, -1.0 to wait for data indefinitely.
1044
1045 </p>
1046 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackChannelWrite">cupsBackChannelWrite</a></h3>
1047 <p class="description">Write data to the backchannel.</p>
1048 <p class="code">
1049 ssize_t cupsBackChannelWrite (<br>
1050 &nbsp;&nbsp;&nbsp;&nbsp;const char *buffer,<br>
1051 &nbsp;&nbsp;&nbsp;&nbsp;size_t bytes,<br>
1052 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1053 );</p>
1054 <h4 class="parameters">Parameters</h4>
1055 <dl>
1056 <dt>buffer</dt>
1057 <dd class="description">Buffer to write</dd>
1058 <dt>bytes</dt>
1059 <dd class="description">Bytes to write</dd>
1060 <dt>timeout</dt>
1061 <dd class="description">Timeout in seconds, typically 1.0</dd>
1062 </dl>
1063 <h4 class="returnvalue">Return Value</h4>
1064 <p class="description">Bytes written or -1 on error</p>
1065 <h4 class="discussion">Discussion</h4>
1066 <p class="discussion">Writes &quot;bytes&quot; bytes to the backchannel/filter. The &quot;timeout&quot; parameter
1067 controls how many seconds to wait for the data to be written - use
1068 0.0 to return immediately if the data cannot be written, -1.0 to wait
1069 indefinitely.
1070
1071 </p>
1072 <h3 class="function"><span class="info">&nbsp;CUPS 1.2/Mac OS X 10.5&nbsp;</span><a name="cupsBackendDeviceURI">cupsBackendDeviceURI</a></h3>
1073 <p class="description">Get the device URI for a backend.</p>
1074 <p class="code">
1075 const char *cupsBackendDeviceURI (<br>
1076 &nbsp;&nbsp;&nbsp;&nbsp;char **argv<br>
1077 );</p>
1078 <h4 class="parameters">Parameters</h4>
1079 <dl>
1080 <dt>argv</dt>
1081 <dd class="description">Command-line arguments</dd>
1082 </dl>
1083 <h4 class="returnvalue">Return Value</h4>
1084 <p class="description">Device URI or <code>NULL</code></p>
1085 <h4 class="discussion">Discussion</h4>
1086 <p class="discussion">The &quot;argv&quot; argument is the argv argument passed to main(). This
1087 function returns the device URI passed in the DEVICE_URI environment
1088 variable or the device URI passed in argv[0], whichever is found
1089 first.
1090
1091 </p>
1092 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsBackendReport">cupsBackendReport</a></h3>
1093 <p class="description">Write a device line from a backend.</p>
1094 <p class="code">
1095 void cupsBackendReport (<br>
1096 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_scheme,<br>
1097 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_uri,<br>
1098 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_make_and_model,<br>
1099 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_info,<br>
1100 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_id,<br>
1101 &nbsp;&nbsp;&nbsp;&nbsp;const char *device_location<br>
1102 );</p>
1103 <h4 class="parameters">Parameters</h4>
1104 <dl>
1105 <dt>device_scheme</dt>
1106 <dd class="description">device-scheme string</dd>
1107 <dt>device_uri</dt>
1108 <dd class="description">device-uri string</dd>
1109 <dt>device_make_and_model</dt>
1110 <dd class="description">device-make-and-model string or <code>NULL</code></dd>
1111 <dt>device_info</dt>
1112 <dd class="description">device-info string or <code>NULL</code></dd>
1113 <dt>device_id</dt>
1114 <dd class="description">device-id string or <code>NULL</code></dd>
1115 <dt>device_location</dt>
1116 <dd class="description">device-location string or <code>NULL</code></dd>
1117 </dl>
1118 <h4 class="discussion">Discussion</h4>
1119 <p class="discussion">This function writes a single device line to stdout for a backend.
1120 It handles quoting of special characters in the device-make-and-model,
1121 device-info, device-id, and device-location strings.
1122
1123 </p>
1124 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelDoRequest">cupsSideChannelDoRequest</a></h3>
1125 <p class="description">Send a side-channel command to a backend and wait for a response.</p>
1126 <p class="code">
1127 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelDoRequest (<br>
1128 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1129 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1130 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1131 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1132 );</p>
1133 <h4 class="parameters">Parameters</h4>
1134 <dl>
1135 <dt>command</dt>
1136 <dd class="description">Command to send</dd>
1137 <dt>data</dt>
1138 <dd class="description">Response data buffer pointer</dd>
1139 <dt>datalen</dt>
1140 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1141 <dt>timeout</dt>
1142 <dd class="description">Timeout in seconds</dd>
1143 </dl>
1144 <h4 class="returnvalue">Return Value</h4>
1145 <p class="description">Status of command</p>
1146 <h4 class="discussion">Discussion</h4>
1147 <p class="discussion">This function is normally only called by filters, drivers, or port
1148 monitors in order to communicate with the backend used by the current
1149 printer.  Programs must be prepared to handle timeout or &quot;not
1150 implemented&quot; status codes, which indicate that the backend or device
1151 do not support the specified side-channel command.<br>
1152 <br>
1153 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1154 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1155 update the value to contain the number of data bytes in the buffer.
1156
1157 </p>
1158 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelRead">cupsSideChannelRead</a></h3>
1159 <p class="description">Read a side-channel message.</p>
1160 <p class="code">
1161 int cupsSideChannelRead (<br>
1162 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> *command,<br>
1163 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> *status,<br>
1164 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1165 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1166 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1167 );</p>
1168 <h4 class="parameters">Parameters</h4>
1169 <dl>
1170 <dt>command</dt>
1171 <dd class="description">Command code</dd>
1172 <dt>status</dt>
1173 <dd class="description">Status code</dd>
1174 <dt>data</dt>
1175 <dd class="description">Data buffer pointer</dd>
1176 <dt>datalen</dt>
1177 <dd class="description">Size of data buffer on entry, number of bytes in buffer on return</dd>
1178 <dt>timeout</dt>
1179 <dd class="description">Timeout in seconds</dd>
1180 </dl>
1181 <h4 class="returnvalue">Return Value</h4>
1182 <p class="description">0 on success, -1 on error</p>
1183 <h4 class="discussion">Discussion</h4>
1184 <p class="discussion">This function is normally only called by backend programs to read
1185 commands from a filter, driver, or port monitor program.  The
1186 caller must be prepared to handle incomplete or invalid messages
1187 and return the corresponding status codes.<br>
1188 <br>
1189 The &quot;datalen&quot; parameter must be initialized to the size of the buffer
1190 pointed to by the &quot;data&quot; parameter.  cupsSideChannelDoRequest() will
1191 update the value to contain the number of data bytes in the buffer.
1192
1193 </p>
1194 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPGet">cupsSideChannelSNMPGet</a></h3>
1195 <p class="description">Query a SNMP OID's value.</p>
1196 <p class="code">
1197 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPGet (<br>
1198 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1199 &nbsp;&nbsp;&nbsp;&nbsp;char *data,<br>
1200 &nbsp;&nbsp;&nbsp;&nbsp;int *datalen,<br>
1201 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1202 );</p>
1203 <h4 class="parameters">Parameters</h4>
1204 <dl>
1205 <dt>oid</dt>
1206 <dd class="description">OID to query</dd>
1207 <dt>data</dt>
1208 <dd class="description">Buffer for OID value</dd>
1209 <dt>datalen</dt>
1210 <dd class="description">Size of OID buffer on entry, size of value on return</dd>
1211 <dt>timeout</dt>
1212 <dd class="description">Timeout in seconds</dd>
1213 </dl>
1214 <h4 class="returnvalue">Return Value</h4>
1215 <p class="description">Query status</p>
1216 <h4 class="discussion">Discussion</h4>
1217 <p class="discussion">This function asks the backend to do a SNMP OID query on behalf of the
1218 filter, port monitor, or backend using the default community name.<br>
1219 <br>
1220 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1221 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1222 supported and must be converted to their numeric forms.<br>
1223 <br>
1224 On input, &quot;data&quot; and &quot;datalen&quot; provide the location and size of the
1225 buffer to hold the OID value as a string. HEX-String (binary) values are
1226 converted to hexadecimal strings representing the binary data, while
1227 NULL-Value and unknown OID types are returned as the empty string.
1228 The returned &quot;datalen&quot; does not include the trailing nul.
1229
1230 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1231 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1232 the printer does not respond to the SNMP query.
1233
1234 </p>
1235 <h3 class="function"><span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span><a name="cupsSideChannelSNMPWalk">cupsSideChannelSNMPWalk</a></h3>
1236 <p class="description">Query multiple SNMP OID values.</p>
1237 <p class="code">
1238 <a href="#cups_sc_status_t">cups_sc_status_t</a> cupsSideChannelSNMPWalk (<br>
1239 &nbsp;&nbsp;&nbsp;&nbsp;const char *oid,<br>
1240 &nbsp;&nbsp;&nbsp;&nbsp;double timeout,<br>
1241 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_walk_func_t">cups_sc_walk_func_t</a> cb,<br>
1242 &nbsp;&nbsp;&nbsp;&nbsp;void *context<br>
1243 );</p>
1244 <h4 class="parameters">Parameters</h4>
1245 <dl>
1246 <dt>oid</dt>
1247 <dd class="description">First numeric OID to query</dd>
1248 <dt>timeout</dt>
1249 <dd class="description">Timeout for each query in seconds</dd>
1250 <dt>cb</dt>
1251 <dd class="description">Function to call with each value</dd>
1252 <dt>context</dt>
1253 <dd class="description">Application-defined pointer to send to callback</dd>
1254 </dl>
1255 <h4 class="returnvalue">Return Value</h4>
1256 <p class="description">Status of first query of <code>CUPS_SC_STATUS_OK</code> on success</p>
1257 <h4 class="discussion">Discussion</h4>
1258 <p class="discussion">This function asks the backend to do multiple SNMP OID queries on behalf
1259 of the filter, port monitor, or backend using the default community name.
1260 All OIDs under the &quot;parent&quot; OID are queried and the results are sent to
1261 the callback function you provide.<br>
1262 <br>
1263 &quot;oid&quot; contains a numeric OID consisting of integers separated by periods,
1264 for example &quot;.1.3.6.1.2.1.43&quot;.  Symbolic names from SNMP MIBs are not
1265 supported and must be converted to their numeric forms.<br>
1266 <br>
1267 &quot;timeout&quot; specifies the timeout for each OID query. The total amount of
1268 time will depend on the number of OID values found and the time required
1269 for each query.<br>
1270 <br>
1271 &quot;cb&quot; provides a function to call for every value that is found. &quot;context&quot;
1272 is an application-defined pointer that is sent to the callback function
1273 along with the OID and current data. The data passed to the callback is the
1274 same as returned by <a href="#cupsSideChannelSNMPGet"><code>cupsSideChannelSNMPGet</code></a>.
1275
1276 <code>CUPS_SC_STATUS_NOT_IMPLEMENTED</code> is returned by backends that do not
1277 support SNMP queries.  <code>CUPS_SC_STATUS_NO_RESPONSE</code> is returned when
1278 the printer does not respond to the first SNMP query.
1279
1280 </p>
1281 <h3 class="function"><span class="info">&nbsp;CUPS 1.3/Mac OS X 10.5&nbsp;</span><a name="cupsSideChannelWrite">cupsSideChannelWrite</a></h3>
1282 <p class="description">Write a side-channel message.</p>
1283 <p class="code">
1284 int cupsSideChannelWrite (<br>
1285 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_command_t">cups_sc_command_t</a> command,<br>
1286 &nbsp;&nbsp;&nbsp;&nbsp;<a href="#cups_sc_status_t">cups_sc_status_t</a> status,<br>
1287 &nbsp;&nbsp;&nbsp;&nbsp;const char *data,<br>
1288 &nbsp;&nbsp;&nbsp;&nbsp;int datalen,<br>
1289 &nbsp;&nbsp;&nbsp;&nbsp;double timeout<br>
1290 );</p>
1291 <h4 class="parameters">Parameters</h4>
1292 <dl>
1293 <dt>command</dt>
1294 <dd class="description">Command code</dd>
1295 <dt>status</dt>
1296 <dd class="description">Status code</dd>
1297 <dt>data</dt>
1298 <dd class="description">Data buffer pointer</dd>
1299 <dt>datalen</dt>
1300 <dd class="description">Number of bytes of data</dd>
1301 <dt>timeout</dt>
1302 <dd class="description">Timeout in seconds</dd>
1303 </dl>
1304 <h4 class="returnvalue">Return Value</h4>
1305 <p class="description">0 on success, -1 on error</p>
1306 <h4 class="discussion">Discussion</h4>
1307 <p class="discussion">This function is normally only called by backend programs to send
1308 responses to a filter, driver, or port monitor program.
1309
1310 </p>
1311 <h2 class="title"><a name="TYPES">Data Types</a></h2>
1312 <h3 class="typedef"><a name="cups_backend_t">cups_backend_t</a></h3>
1313 <p class="description">Backend exit codes</p>
1314 <p class="code">
1315 typedef enum <a href="#cups_backend_e">cups_backend_e</a> cups_backend_t;
1316 </p>
1317 <h3 class="typedef"><a name="cups_sc_bidi_t">cups_sc_bidi_t</a></h3>
1318 <p class="description">Bidirectional capabilities</p>
1319 <p class="code">
1320 typedef enum <a href="#cups_sc_bidi_e">cups_sc_bidi_e</a> cups_sc_bidi_t;
1321 </p>
1322 <h3 class="typedef"><a name="cups_sc_command_t">cups_sc_command_t</a></h3>
1323 <p class="description">Request command codes</p>
1324 <p class="code">
1325 typedef enum <a href="#cups_sc_command_e">cups_sc_command_e</a> cups_sc_command_t;
1326 </p>
1327 <h3 class="typedef"><a name="cups_sc_connected_t">cups_sc_connected_t</a></h3>
1328 <p class="description">Connectivity values</p>
1329 <p class="code">
1330 typedef enum <a href="#cups_sc_connected_e">cups_sc_connected_e</a> cups_sc_connected_t;
1331 </p>
1332 <h3 class="typedef"><a name="cups_sc_state_t">cups_sc_state_t</a></h3>
1333 <p class="description">Printer state bits</p>
1334 <p class="code">
1335 typedef enum <a href="#cups_sc_state_e">cups_sc_state_e</a> cups_sc_state_t;
1336 </p>
1337 <h3 class="typedef"><a name="cups_sc_status_t">cups_sc_status_t</a></h3>
1338 <p class="description">Response status codes</p>
1339 <p class="code">
1340 typedef enum <a href="#cups_sc_status_e">cups_sc_status_e</a> cups_sc_status_t;
1341 </p>
1342 <h3 class="typedef"><a name="cups_sc_walk_func_t">cups_sc_walk_func_t</a></h3>
1343 <p class="description">SNMP walk callback</p>
1344 <p class="code">
1345 typedef void (*cups_sc_walk_func_t)(const char *oid, const char *data, int datalen, void *context);
1346 </p>
1347 <h2 class="title"><a name="ENUMERATIONS">Constants</a></h2>
1348 <h3 class="enumeration"><a name="cups_backend_e">cups_backend_e</a></h3>
1349 <p class="description">Backend exit codes</p>
1350 <h4 class="constants">Constants</h4>
1351 <dl>
1352 <dt>CUPS_BACKEND_AUTH_REQUIRED </dt>
1353 <dd class="description">Job failed, authentication required</dd>
1354 <dt>CUPS_BACKEND_CANCEL </dt>
1355 <dd class="description">Job failed, cancel job</dd>
1356 <dt>CUPS_BACKEND_FAILED </dt>
1357 <dd class="description">Job failed, use error-policy</dd>
1358 <dt>CUPS_BACKEND_HOLD </dt>
1359 <dd class="description">Job failed, hold job</dd>
1360 <dt>CUPS_BACKEND_OK </dt>
1361 <dd class="description">Job completed successfully</dd>
1362 <dt>CUPS_BACKEND_RETRY </dt>
1363 <dd class="description">Job failed, retry this job later</dd>
1364 <dt>CUPS_BACKEND_RETRY_CURRENT </dt>
1365 <dd class="description">Job failed, retry this job immediately</dd>
1366 <dt>CUPS_BACKEND_STOP </dt>
1367 <dd class="description">Job failed, stop queue</dd>
1368 </dl>
1369 <h3 class="enumeration"><a name="cups_sc_bidi_e">cups_sc_bidi_e</a></h3>
1370 <p class="description">Bidirectional capability values</p>
1371 <h4 class="constants">Constants</h4>
1372 <dl>
1373 <dt>CUPS_SC_BIDI_NOT_SUPPORTED </dt>
1374 <dd class="description">Bidirectional I/O is not supported</dd>
1375 <dt>CUPS_SC_BIDI_SUPPORTED </dt>
1376 <dd class="description">Bidirectional I/O is supported</dd>
1377 </dl>
1378 <h3 class="enumeration"><a name="cups_sc_command_e">cups_sc_command_e</a></h3>
1379 <p class="description">Request command codes</p>
1380 <h4 class="constants">Constants</h4>
1381 <dl>
1382 <dt>CUPS_SC_CMD_DRAIN_OUTPUT </dt>
1383 <dd class="description">Drain all pending output</dd>
1384 <dt>CUPS_SC_CMD_GET_BIDI </dt>
1385 <dd class="description">Return bidirectional capabilities</dd>
1386 <dt>CUPS_SC_CMD_GET_CONNECTED <span class="info">&nbsp;CUPS 1.5&nbsp;</span></dt>
1387 <dd class="description">Return whether the backend is &quot;connected&quot; to the printer </dd>
1388 <dt>CUPS_SC_CMD_GET_DEVICE_ID </dt>
1389 <dd class="description">Return the IEEE-1284 device ID</dd>
1390 <dt>CUPS_SC_CMD_GET_STATE </dt>
1391 <dd class="description">Return the device state</dd>
1392 <dt>CUPS_SC_CMD_SNMP_GET <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1393 <dd class="description">Query an SNMP OID </dd>
1394 <dt>CUPS_SC_CMD_SNMP_GET_NEXT <span class="info">&nbsp;CUPS 1.4/Mac OS X 10.6&nbsp;</span></dt>
1395 <dd class="description">Query the next SNMP OID </dd>
1396 <dt>CUPS_SC_CMD_SOFT_RESET </dt>
1397 <dd class="description">Do a soft reset</dd>
1398 </dl>
1399 <h3 class="enumeration"><a name="cups_sc_connected_e">cups_sc_connected_e</a></h3>
1400 <p class="description">Connectivity values</p>
1401 <h4 class="constants">Constants</h4>
1402 <dl>
1403 <dt>CUPS_SC_CONNECTED </dt>
1404 <dd class="description">Backend is &quot;connected&quot; to printer</dd>
1405 <dt>CUPS_SC_NOT_CONNECTED </dt>
1406 <dd class="description">Backend is not &quot;connected&quot; to printer</dd>
1407 </dl>
1408 <h3 class="enumeration"><a name="cups_sc_state_e">cups_sc_state_e</a></h3>
1409 <p class="description">Printer state bits</p>
1410 <h4 class="constants">Constants</h4>
1411 <dl>
1412 <dt>CUPS_SC_STATE_BUSY </dt>
1413 <dd class="description">Device is busy</dd>
1414 <dt>CUPS_SC_STATE_ERROR </dt>
1415 <dd class="description">Other error condition</dd>
1416 <dt>CUPS_SC_STATE_MARKER_EMPTY </dt>
1417 <dd class="description">Toner/ink out condition</dd>
1418 <dt>CUPS_SC_STATE_MARKER_LOW </dt>
1419 <dd class="description">Toner/ink low condition</dd>
1420 <dt>CUPS_SC_STATE_MEDIA_EMPTY </dt>
1421 <dd class="description">Paper out condition</dd>
1422 <dt>CUPS_SC_STATE_MEDIA_LOW </dt>
1423 <dd class="description">Paper low condition</dd>
1424 <dt>CUPS_SC_STATE_OFFLINE </dt>
1425 <dd class="description">Device is offline</dd>
1426 <dt>CUPS_SC_STATE_ONLINE </dt>
1427 <dd class="description">Device is online</dd>
1428 </dl>
1429 <h3 class="enumeration"><a name="cups_sc_status_e">cups_sc_status_e</a></h3>
1430 <p class="description">Response status codes</p>
1431 <h4 class="constants">Constants</h4>
1432 <dl>
1433 <dt>CUPS_SC_STATUS_BAD_MESSAGE </dt>
1434 <dd class="description">The command/response message was invalid</dd>
1435 <dt>CUPS_SC_STATUS_IO_ERROR </dt>
1436 <dd class="description">An I/O error occurred</dd>
1437 <dt>CUPS_SC_STATUS_NONE </dt>
1438 <dd class="description">No status</dd>
1439 <dt>CUPS_SC_STATUS_NOT_IMPLEMENTED </dt>
1440 <dd class="description">Command not implemented</dd>
1441 <dt>CUPS_SC_STATUS_NO_RESPONSE </dt>
1442 <dd class="description">The device did not respond</dd>
1443 <dt>CUPS_SC_STATUS_OK </dt>
1444 <dd class="description">Operation succeeded</dd>
1445 <dt>CUPS_SC_STATUS_TIMEOUT </dt>
1446 <dd class="description">The backend did not respond</dd>
1447 <dt>CUPS_SC_STATUS_TOO_BIG </dt>
1448 <dd class="description">Response too big</dd>
1449 </dl>
1450 </div>
1451 </body>
1452 </html>